Particle contamination can be a significant problem in semiconductor manufacturing. A photomask is typically protected from contaminating particles by a pellicle, a thin transparent film stretched over a frame that is glued over one side of the photomask. The pellicle is far enough away from the mask patterns so that moderate-to-small sized particles that land on the pellicle will be too far out of focus to print. Although they are designed to keep particles away, pellicles become a part of the imaging system and their optical properties effect the lithography and are taken into account.
Conventionally, a pellicle can be used to protect and prevent contamination of the patterned side of ultraviolet (e.g., using 193 nm argon fluorine exciplex lasers) optical lithography masks. However, extreme ultraviolet (EUV) lithography does not allow the use of a pellicle due to the optical effects of the pellicle. However, if the bare mask is not handled properly, there is a risk of contamination.
Thus, EUV masks (without the protection of a pellicle) are typically only handled in a vacuum. For example, a mask carrier with a nested inner carrier that conforms to the SEMI E152 standard provides double isolation of the bare mask for contamination control, with the assumption that the inner carrier will only be opened in a vacuum. However, an inner carrier opener in a vacuum presents significant cost and complexity. Thus, what is needed are methods and systems that facilitate mask handling without requiring nested carriers and vacuum isolation.